SUMMARY While the mechanisms modulating the transmission and perception of chronic pain differ between men and women, the exact neuroanatomical and molecular differences existing between the sexes remain only partly understood. This proposal focuses on the study of intracellular mechanisms that modulate symptoms of long-term pain states in female mice. We have identified signal transduction mechanisms in the mouse ventrolateral periaqueductal gray (vlPAG) that selectively modulate sensory symptoms of inflammatory and neuropathic pain in female mice. The signal transduction modulator Regulator of G Protein Signaling-1 (RGSz1) controls the function of G protein coupled receptors (GPCRs) by binding to activated G?i subunits, including the Golgi enriched G?z. RGSz1 negatively modulates the amplitude and direction of signal transduction of several GPCRs involved in the modulation of pain processing, including the serotonin 5HT1A receptor. We recently found that RGSz1 mRNA and protein levels are dynamically regulated in the vlPAG of female (but not male) mice by long-term peripheral inflammation. Constitutive deletion of the RGSz1 gene or vlPAG-specific knockdown of RGSz1, exacerbate sensory hypersensitivity behaviors such as thermal hyperalgesia and mechanical allodynia in female mice, but they have no effect in male mice. We will investigate the mechanisms regulating the expression of RGSz1 in the male and female vlPAG at various points after the induction of peripheral nerve injury or inflammation. We will apply several genetic mouse models for regional inactivation or overexpression of RGSz1 in vlPAG neuronal subsets, along with brain biochemistry, electrophysiology and voltammetry to understand the sex-specific role of RGSz1 in the function of the descending inhibitory pathway in models of chronic pain. Since RGSz1 plays a prominent role in the function of the Golgi apparatus, will apply chronic pain models to understand the impact of RGSz1 on the expression levels of trans- Golgi components in the presence and in the absence of pain. Finally, we will use RNA Sequencing to understand the impact of RGSz1 on gene expression adaptations underlying chronic pain states.